The glomerular basement membrane forms the boundary between blood and urine. Across it, water and other small molecules from the blood are filtered. The GBM is composed of a meshwork of proteins and other constituents. Type IV collagen and laminin are present in the largest quantities. Some specialized subtypes of these molecules are only found in specialised basement membranes such as the GBM.
Thin GBM disease
Thin glomerular basement membrane disease is the thinning of the basement membrane of the glomerulus. The GBM is thin, and must sometimes break, as it causes blood to appear in the urine. However it seems to repair without any ill effect, as thin GBM disease almost never causes serious trouble. The condition often runs in families, and can be a cause of benign familial haematuria.